AIRCRAFT TIRES AND AIR PRESSURE

THE WHY'S AND HOW'S

                                                                  A SENSE OF URGENCY

No other tires in the world are required to carry the heavy loads and high speeds as that of an aircraft tire. Proper air pressure
maintenance is a must for an Airline to achieve optimum performance of its tires. This document will discuss the why's and how's
in layman's language of an often underrated subject.

A CHANGING WORLD

Airlines today face many unique factors that have impacted the maintenance of aircraft tires. Some of the major factors include:
1. Aircraft manufactures are extremely weight conscious; therefore, in many instances tires at best are marginal for load/speed and
maneuvers required.
2. Schedule demands often require high speed exits off the first ramp.
3. Due to limited available space at gates, locked wheel pivots are the norm rather than the exception.
4. Scheduling of aircraft at times leaves aircraft at “out station" airports where tire maintenance is difficult to perform.
5. Intense scheduling of aircraft during daily operations prevents the desired "cool-down" period of landing gear components.
6. Education of airline personnel by manufacturers and suppliers must be intensified to the level necessary to insure that proper
maintenance is being performed as times and conditions change.

                                                             LOW AIR PRESSURE YIELDS
Low air pressure operation creates
conditions that generate excessive heat.
This example shows excessive shoulder
wear.
Excessive heat can lead to separations .Observe bubbles.
Total failure can be the result of an undetected separation, leading to downtime and possible equipment
damage.
                  Proper air pressure maintenance and detection can prevent most tire
failures!
                                         ROUTINE AND NORMAL AIR LOSS
VENT HOLES AND NORMAL DIFFUSION
Vent holes or weep holes are small needle holes made in the lower sidewall of the tire above the bead. Vent holes are
marked with green litho ink or paint and penetrate to the mid casing. They provide an escape path to the atmosphere for
any nitrogen which has permeated naturally through the inner liner and would otherwise become trapped within the tire
and cause ply or tread separation.

Seepage of gas (air) from the vent holes is normal and should be seen when the wheel assembly is immersed or
soapy water applied.

PRESSURE LOSS DUE TO TIRE GROWTH
Due to the properties of the materials from which they are constructed, aircraft tires will grow for up to 12 hours after
initial inflation. As the volume of the tire increase, as a consequence of this growth, the effective pressure will reduce.

THE INFLATION PRESSURE OF NEWLY MOUNTED TIRES SHOULD BE CHECKED AFTER A
MINIMUM OF 12 HOURS AND RE-INFLATED TO THE REQUIRED PRESSURE.

PROPER INSTALLATION PROCEDURES

1. INFLATE TIRE TO NORMAL OPERATING PRESSURE.

2. AFTER 12 HOURS, RE-INFLATE TO NORMAL OPERATING PRESSURE, REFERRED TO AS STRETCH PERIOD

3. AFTER 24 HOURS. CHECK AIR PRESSURE: LESS THAN 5% AIR LOSS-TIRE ACCEPTABLE.
MORE THAN 5%-REJECT.

4. MONITOR PRESSURE EVERY 24 HOURS AND INFLATE TO CORRECT-PRESSURE.

OTHER CAUSES OF AIR PRESSURE LOSS

TIRES ARE NOT ALWAYS THE CAUSE OF LOW AIR PRESSURE. OTHER POSSIBILITIES INCLUDE:
* Leaks at valve stem or valve core.
* Leaks at valve seal.
* O Ring.
* Fuse Plug.
* Bead seepage between wheel flange and tire.
* Porosity-leaking through the well area of the wheel.
* Cut or puncture.
* Damage to the tire liner.
* A lowering of the air temperature.

IN-SERVICE PROCEDURES
It is essential that aircraft tires be maintained at the correct inflation pressure. Under inflation of tires can result in
higher than normal stresses causing a reduction in the carcass life of the tire or possible failure in service. Pressure
should be checked and adjusted only when tires are at ambient temperature. Due to diffusion of gas through the inner
liner of the tire pressure can reduce by up to 5% in 24 hours. Where practical;

AIR PRESSURE SHOULD BE MADE USING AN ACCURATE DIAL TYPE GAUGE AT LEAST ON A DAILY BASIS!

ACTION REQUIRED FOR TIRES BELOW SPECIFIED INFLATION PRESSURE
95%-100% Inflate tire to specified pressure plus maximum tolerance.

90%-95% Check aircraft log.

If no previous record, inflate tire to specified pressure plus maximum tolerance and record in aircraft log.
Remove tire if last record also indicated low pressure.

Less than 90% remove tire.

Less than 80% remove tire and mate.
WEAR PATTERNS RELATIONSHIP TO AIR PRESSURE

Excessive wear may be seen at both shoulders of the tire. This normally occurs as a result of under inflation of the tire.








Excessive wear may be seen at the center of the tire. This normally occurs as a result of over pressurization of the tire.






                                                                               The perfect worn tire!
















Proper Air Pressure practices will not only yield less opportunities for tire failure; but will
enhance tire life, landing performance and schedule reliability; saving an airline both time
and money! It's worth the extra care!

This document was prepared by James L. and William E. (Bill) Wilkerson of the Wilkerson Company; Inc. of Crewe, Va.

ABOUT THE WILKERSON COMPANY

Wilkerson Company, Inc. is one of four licensed high speed aircraft tire retreaders in the United States. One hundred
thousand aircraft tires will be shipped out of Crewe, Va in 2017; including 60,000 retreads and 40,000 new Goodyear
and Dunlop aircraft tires. According to Independent Market Analysis, WCO services 85% of the Regional Commuter
Airlines in the United States and Canada. WCO also services more than 90 countries and territories in the international
market. FAA statistics indicate that aircraft using WCO retreads will take-off and land 18,000,000 times a year. WCO
grew up with the very first Regional Airlines and Flight Schools in the 1960's; therefore, our experience in the industry can
work for you.

Credits and Reference Materials

"THE COMPREHENSIVE GUIDE TO AIRCRAFT TIRE CARE AND MAINTENANCE" published by The Goodyear Tire and
Rubber Company.

"GENERAL SERVICING INSTRUCTIONS AIRCRAFT TYRES AND TUBES" published by Dunlop Limited Aircraft Tyres
Division

To Contact the authors you may use any one of the following methods:

Phone: 434-645-9641

Fax: 434-645-7759

E-Mail:
sara@wilkersonaircrafttires.com

Mail: Wilkerson Company, Inc. P. O. Box 438 Crewe, Va. 23930
WILKERSON AIRCRAFT TIRES OF CREWE, VA
206 West Virginia Avenue
Crewe, Va 23930
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